The present application is based upon and claims priority to Japanese Patent Application No. 11-274736, filed Sep. 28, 1999, the entire contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to small watercraft, and in particular to a hull construction for a small watercraft.
2. DESCRIPTION OF THE RELATED ART
Personal watercraft have become very popular in recent years. A personal watercraft is designed to be operated by a rider who sits in a straddle-like fashion at a central position on the watercraft. Some personal watercrafts also have seating for one or two passengers. For this purpose, the personal watercraft includes an upper deck section with an elongated bench which the rider and passengers straddle. The deck also includes foot areas that extend along both sides of the bench.
Over the past few years, a lower section of the personal watercraft hull has steadily evolved in an effort to optimize the speed and the handling of the small watercraft. The hull lower section now commonly has a deep xe2x80x9cVxe2x80x9d shape and often includes one or more inner chines or strakes between a keel line of the hull and the outer chines. The lower hull section is designed such that the watercraft planes or rides on only a portion of the lower hull section""s surface area at the aft end of the watercraft. The wetted area of the watercraft hull (i.e., the portion of the watercraft hull in contact with the water) desirably is small in comparison to the total surface area of the hull lower section in order to reduce drag on the watercraft. For this purpose, the watercraft""s bow rises out of the water to reduce the wetted area when the watercraft is planing.
The angle formed between the bow and the surface of the body of water in which the watercraft is operated affects the drag or resistance experienced by the watercraft hull as it planes over the water surface. This angle is often referred to as the planing angle of the watercraft. Too large or small of an angle significantly increases drag on the watercraft hull. An optimal planing angle therefore exists in order to minimize drag on the watercraft.
Prior hulls, however, most often are designed to raise the watercraft hull to a smaller than the optimum planing angle for the watercraft in order to minimize pitching of the watercraft. Prior watercrafts tend to pitch severely when planing with the bow raised to the optimum-planing angle. That is, the bow of the watercraft tends to bounce up and down with the bow raised out of the water to the desired planing angle. This condition is commonly referred to as xe2x80x9cporpoisingxe2x80x9d and produces a very uncomfortable ride. In addition, watercraft speed suffers because bow porpoising increases the drag on the watercraft. At a smaller angle, the watercrafts does not porpoise to a meaningful extent; however, drag on the watercraft increases with a smaller angle as compared with the planing optimum angle if it could be maintained.
A recent hull design included a stepper at the aft end of the hull in order to improve the stability of the watercraft when planing at the desired planing angle. A stepper is a vertical rise in the hull surface, as will be explained below in detail. The stepper reduces the wetted surface of the watercraft hull while effectively elongating the hull in order to improve the stability of the watercraft.
Recent designs have included a pair of steppers and a rounded transom in order to further stabilize the watercraft when up on plane and thereby inhibit porpoising of the watercraft when running at high speeds. Such an aft hull design further reduces the wetted area of the watercraft hull when up on plane, while supporting the aft end of the deck and providing buoyancy at the watercraft aft end when in a static state. The dual stepper hull design also provides a rocker effect that permits the rider to pull the watercraft bow up earlier when jumping, for improved watercraft handling.
The present hull configuration incorporates a pair of stepper area plates (step plates) attached to the first stepper area in such a manner as to create a gap between the first stepper and the leading end of each step plate. The gap has an outer end portion that terminates towards the lateral side of the hull to allow communication with atmospheric air. When the watercraft is up on plane, the opening is preferably above the water surface and atmospheric air is drawn into the opening by the venturi action from water passing over the gap. The drawn-in air mixes with the water passing over the step plate and has the effect of reducing the drag on the rear portion of the hull. In one mode, longitudinal channels are provided on the step plate to increase the air drawn into the opening while decreasing the plate surface area to further reduce drag. In an additional mode, the amount of drawn air is increased or supplied by providing at least one supplemental aperture in the downward facing surface of the gap. A hose is connected to the aperture and communicates with the atmosphere (e.g., the air within the engine compartment). The placement of the inlet portion of the hose inhibits the entry of water into the hose to maximize supplemental drawn air and further reduce drag.
Thus, in accordance with one aspect of the present invention, a hull for a planing-watercraft includes a pair of inclined sections arranged generally in a v-shape. The inclined sections extend generally along a longitudinally extending central axis from a front portion of the hull toward a rear portion of the hull. The hull further includes at least a first arrangement of surfaces. The first arrangement of surfaces includes a first surface and a second surface. The second surface is positioned rearward of the first surface so as to create a gap between the first and second surfaces. The gap extends from an outer portion of the surfaces to an inner portion of the surfaces in a lateral direction that is generally normal to the centerline of the hull.
Another aspect of the present invention involves a jet propelled watercraft comprised of a hull and a jet propulsion unit that is mounted in the hull and has a downwardly facing water inlet opening through which water is drawn. The jet propulsion unit further includes a discharge nozzle. The hull is comprised of an upper deck and a lower hull with an engine compartment defined at least in part within the lower hull. The lower hull including a first arrangement of surfaces that is disposed rearward of the water inlet opening. The first arrangement of surfaces includes a first surface and a second surface. The second surface is positioned rearward of the first surface so as to create a gap between the first and second surfaces. The lower hull also includes a source of air communicating with the gap. In one mode, the source of air is provided by the outer lateral end of the gap extending toward and preferably proximate to a lateral side of the hull so as to be above the water surface level when the watercraft is up on plane. Air is drawn through this open end of the gap by the venturi effect. In other modes, the source of air can include one or more air supply apertures communicating with the gap.
An additional aspect of the present invention involves a step plate for use on a planing watercraft hull. The hull being of the type that has at least one stepper formed in a lower portion of the hull, at least one stepper area formed on an aft side of the stepper, and a ride plate mounted to the hull in a central rearward location. The step plate has at least one longitudinally extending channel. The step plate also is mounted to the stepper area on either side of the ride plate.
Further aspects, features and advantages of the present hull construction will become apparent from the description of the preferred embodiments of the hull that follow.